Fire detector cable



Dec' 24, 1946. L. H. VWALBRIDGE 2,413,125

FIRE DETECTOR CABLE Filed Dec. 3l, 1945 lPatentedl Dec. 24, 1946 2,413,125 ma DETECTOR CABLE Lyman H. Walbridge, Ashland, Mass., assignor to Fenwai Incorporated, Ashland, Mass., a corporation of Massachusetts Application December 31, 1943, Serial No. 516,605

4 Claims. Cl. 201-83) This invention relates to lire detector cables oi the type wherein an undue rise in temperature at any point in the protected area will close a normally opened circuit.

the said elements closely ittlng the tube. Interposed between the wire I l andthe tube is a quantity of sodium nitrate or potassium nitrate, or other suitable material, in dry form, preferably When lire detector cables having a conductor 5 powder, as indicated at I3.

enclosed within a tube and insulated therefrom In the embodiment of my invention shown in by closely spaced insulation bodies' are placed Fig. 2, the wire Il is surrounded by a mass of suitaround the walls of a restricted space, such as able non-combustible porous material which, in the cockpit of an airplane, it has been found that the present instance, is shown as a cylinder i3' the sharp bends to which the tubes are subjected l of asbestos, or the like, which is impregnated with will cause the insulation bodies to crack and a solution of potassium nitrate, sodium nitrate, otherwise impair the operation of the cable. or any other suitable salt which is non-conduct- `The object, therefore, of the present invention ing at low temperature and conducting at abnorls to provide a re detector cable which has suilimal temperatures. cient iiexibility to enable it to be bent on a small l An alarm circuit ls indicated diagrammatically radius of curvature without injury. I have disand includes the battery I I, or other source of covered that certain salts in dry form are elecvoltage, and an alarm or indicating device I5, trically non-conductive at normal temperatures the terminals of said circuit being conducted to and electrically conductive at abnormal temperathe tube I0 and conductor Il. tures, and that such salts may be employedv to In bOth Figs- 1 and 2J the jagged lines 9J? the insulate an electrical conductor from a conductive ends of the tube and the conductor indicate that tube surrounding the same so that an alarm cirthe cables are of indefinite lengths. Each cable, cuit having its terminals connected to the tube throughout its entire length, has Sllcient ilexiand conductor will remain open at normal tembility to permit of bending on a small radius of peratures and will be closed at abnormal or lire 26 curvature without injury either to the tubing temperatures, the salt melting or partially meltmember or the elements enclosed therein, whereby ing to ailord a conductive path between the tube liability to short circuit is effectively eliminated. and its enclosed conductor, At normal temperatures the circuit of the in- The enclosed conductor may be insulated medicator will be' open and at abnormal temperachanically from the enclosed tube by spaced in- 30 tures, it will be closed through the conducting sulators and the spaces between the latter filled path aiorded by the material interposed between with the proper salt in dry form, or the enclosed the tube and thecond-uctor enclosed therein. conductor may be insulated with asbestos or other The term normal temperature is used in the suitable insulating material impregnated with a specication and claims as dening a temperature solution of such salt. I have ascertained that polower than that which is generally known in this tassium nitrate and sodium nitrate in dry or powart as llame temperature. and the term abdered form are non-conducting at ordinary temnormal temperature, as defining llame temperatures and that they melt or partially melt perature or a temperature higher than the same. and thereby become conducting at higher tem- Having thus described illustrative embodiments peratures. These Salts are typical and characof my invention without, however, limiting the teristic of those that can be used in the present same thereto, what I claim and desire to secure invention as they are stable and have relatively by Letters patent is; low melting points. 1. A readily bendable conductor cable of in- In the accompanying drawing, deilnite continuous length for detection of ab- Flgure 1 is a central longitudinal 'section of a 45 normal temperature conditions at any location re detector Cable embdying my invention and adjacently along it, comprising an electrically Fig. 2 is a similar section of another embodiment conductive tubing element adapted for bending thereof. on a relatively small radius of curvature, an un- In the drawing selected to more fully disclose insulated electrical conductor extending continuthepliniple underlying myinventin, |015 atube ously through and spaced from said tubing ele- Of Suitable metal, Such as Copper. and Il 1S an ment, discontinuous non-conductive means inuninsulated conductor disposti within said tube tei-engaging said conductor and tubing element and Passing through apertures in spaced insulatand maintaining the spacing thereof subject to ins elements I2, herein shown as spherical. albending of the cable, and in the spaces between though they may have any other suitable shape. u said conductor, said tubing element and said nonantenas conductive means, a substantially lling quantity ously through and spaced fro lsaid tubing eieoi non-gaseous material which is electrically non= ment, discontinuous non-conductive means interconductive normal temperatures electricengaging said conductor and tubing element and ally conductive at abnormal tempera i.; maintaining the spacing thereof subject to bend- 2. A readily bendable conductor cable ci in-n 5 ing of the cable, and in the spaces between said definite continuous length for detection of abnorconductor, said tubing element and said non-conmai temperature conditions at any location adductive means, a substantially filling quantity of jacently along it, comprising an electrically consodium nitrate in dry for-m.

ductive tubing element adapted for bending on e. A readily bendable conductor cable of in- .i

a relatively small radius of curvature, an uninl0 definite continuous length for detection ci absulated electrical conductor extending continunormal temperature conditions at any location ously through and spaced lrom said tubing eleadiacently along it, comprising an electrically ment, discontinuous non-conductive means interconductive tubing element adapted for bending on engaging said conductor and tubing element and a relatively small radius ot curvature, an uninniaintaining the spacing thereof subject to bend- 15 sulated electrical conductor extending continu.- ing oi the cable, and in the spaces between said ously through and spaced from said tubing eleconductor, said tubing element and said nonment, :means interengaging said conductor and conductive means, asubstantially filling quantity tubing element and maintaining the spacing of potassium nitrate in dry form. thereof subject to bending of the cable, said means 3. A readily bendable conducto cable oi. in- 20 comprising a non-combustible porous nongase= definite continuous length for detection of abous material impregnated with asubstance which normal temperature conditions at any location is electrically no -conductive at normal temadjacently along it, comprising an electrically peratures and electrically conductive at abnormal conductive tubing element adapted for bending temperatures. on a relatively small radius of curvature, an un- 25 insulated electrical conductor extending continui-I 

